Sorry, what I meant is that a flipped delver, as just a 3/2, needs evasion, but Gurmag Angler, as a 5/5, generally doesn't. So the extra mana cost of Tombstalker in exchange for flying generally isn't worth it. We're on the same page here.
My thoughts: 5 is significantly less than 6 in an actual game, but 8 is significantly more than 6 also! These thoughts aren't very sophisticated. I expect this one will see much more constructed play than Phyrexian Rebirth, which, to be fair, if memory serves had to compete with the likes of...
I logged on to /r/magicTCG for the first time in over a year to see if there were new BFZ spoilers, and there was a post about grid drafting.
https://www.reddit.com/r/magicTCG/comments/3jy974/little_twist_on_grid_draft_for_two_players_using/
Then I googled "grid draft" and "grid drafting" and...
I think in Modern, at least, that there are so few permanents on the board that the evasion doesn't make a huge difference. 5/5 is going to rumble in anyways, very few creatures there can block it. It's not like Delver that needs the evasion to swing in without trading. Although the deck runs...
I gotta say, it's kind of crazy how much people play Tombstalker with a {B} reduction and no flying. Considering Tombstalker was getting precisely 0 play.